Partial discharge damage mechanisms in laminated oil-paper insulation

Abstract

The insulation of oil-immersed paper bushing in a transformer bushing is mainly made of multi-layer paper insulation. This work investigates the whole process from discharge initiation to breakdown of an oil-paper insulation model. On the basis of establishing a laminated insulation test sample of a capacitive bushing immersed in oil paper as found in an analogue transformer, a constant voltage method was used to pressure-test to breakdown of the insulation paper. After the analysis of carbon marks on the surface, internal fibre structure, surface functional groups, and surface element content, the results show that: during each stage of partial discharge, the area of carbon marking on the surface of the insulation paper decreases gradually from high the voltage electrode to the ground electrode on a layer-by-layer basis, the extent of damage to the fibre surface and molecular chain is reduced, and the tendency to carbonisation is weakened. With increasing partial discharge time, the area of the carbon mark on the surface of the insulation paper increased layer-by-layer, the damage to the fibre surface and molecular chain increased, and the tendency to carbonisation increased. These results provide a guidance to those interested in the partial discharge mechanism of multi-layer insulation paper.